To me, a session isn't a singaround, and songs etc. are a rarity. I'm talking mainly about Irish sessions I've known in the UK and Ireland over the last 30 years or so.

Applause is rare, too, reserved for, say, a really outstanding solo. The musicians are playing mainly for each other, not to entertain the punters, who are there because they like the ambience. And they seldom applud each other- friendly ragging is more likely. Though a good crowd makes a good session, they are still largely tangential to the whole effort.

Although it's obviously staged, I think the CD "Music At Matt Molloy's" is a good evocation of session atmosphere, complete with the music getting ragged as the musicians get 'tired'.